Gov. Rick Scott declared a health emergency in four counties Wednesday after at least nine cases of the mosquito-borne Zika illness were detected in Florida.

Health officials believe all of the cases are from people who contracted the disease while traveling to affected countries.

"We have to ensure Florida is prepared and stays ahead of the spread of the Zika virus in our state," Scott said in a statement. "We know that we must be prepared for the worst even as we hope for the best."

Scott signed the order Wednesday to cover Miami-Dade, Lee, Hillsborough and Santa Rosa counties.

The Zika virus is linked to brain deformities in babies and is causing concern among public health officials worldwide – the World Health Organization declared an international emergency on Monday, calling the virus a "public health threat." The virus is primarily spread through mosquito bites, but investigators had been exploring the possibility it could be sexually transmitted.

U.S. health officials say a person in Texas became infected with Zika through sex, in the first case of the illness being transmitted within the United States.